This invention relates to cover plates for switches and electrical outlets and particularly to a cover plate assembly wherein the cover plate is mounted such that no mounting screws are visible.
Electrical circuit devices such as switches and electrical outlets for receiving standard electrical plugs are usually mounted within wall boxes mounted in an opening in a wall such that only a small portion of the electrical circuit device protrudes outward from the surface of the wall. Wires connecting the electrical devices to sources of power, ceiling lights, or other remotely situated electrical equipment are generally positioned within the wall and coupled to the electrical devices situated within the box. Each electrical circuit device is typically mounted to the box by a pair of screws engaging threaded holes in a pair of tabs integrally provided with the wall box. The threaded holes in the tabs of the wall box are provided at a standard distance from each other to be capable of receiving a wide variety of standard electrical circuit devices.
A conventional cover plate is generally provided with one or more openings for receiving any projecting portion of the wall box mounted electrical circuit device. The cover plate additionally includes one or more openings for receiving screws for fastening the cover plate to the electrical circuit device to cover the wall box and a portion of the wall immediately surrounding the box. Conventional cover plates can be made of a variety of materials including plastic or metal and can be decorated to harmonize with the surrounding decor. Unfortunately, the visible presence of the mounting screws tends to interrupt the otherwise acceptable appearance of the cover plate.
Some prior cover plate assemblies have been designed which eliminate any visible mounting screws. For example, U.S. Pat. No. 3,953,933 discloses a cover plate assembly which consists of a first member adapted to be mounted by screws to the electrical device mounted in the wall box. The first member integrally includes a frame defining portion located at the perimeter of the first member. A decorative second member, the first member is received within the frame defining portion to cover the screws mounting the first member to the electrical device. A plurality of resilient fingers provided on the interior of the frame of the first member resiliently engage the perimeter of the second member to retain the two members in position.
Another example is found in U.S. Pat. No. 3,987,928 which discloses a first or intermediate plate member fixed to the electrical device mounted in the wall box by screws, the first member having a plurality of apertures at selected spaced locations. A decorative cover plate is provided which includes a plurality of integral rods projecting rearwardly from the back surface of the cover plate, the rods being situated to project through and frictionally engage the apertures in the intermediate plate. The outer perimeter of the cover plate lies flush with the wall surrounding the box when the lugs are fully received in the intermediate plate apertures. A similar mounting scheme is also disclosed in U.S. Pat. Nos. 4,835,343 and 5,180,886 except that the integral rearward projecting members are included on a perimeter defining member having a central opening for receiving adapter plates of a variety of designs.
Yet another example is found in U.S. Pat. No. 4,800,239 which discloses a decorative switch plate assembly wherein a base plate having a recessed perimeter is secured to the electrical devices mounted in the wall box by means of the usual mounting screws. One or more decorative plates are then situated on top of the base plate to obscure the presence of the screws. A frame member envelopes the perimeter of the decorative plates and snaps over the base plate with a plurality of small inward projections on the frame member the recessed edge of the base plate.
All of the previously mentioned designs rely on a frictional engagement of projections of one character or another to hold the final cover plate in place to hide the underlying screws. In the event of repeated removal and reinstallation of the final cover plate, the frictional engagement can become diminished or fail completely due to wear or breakage of the projections often mandating replacement of the cover plate assembly as a whole. The present invention seeks to avoid the use of wearable or breakable projections while achieving a secure and safe cover plate assembly having no visible means of attachment.